1. Field of the Invention
This invention relates to a front emission type fluorescent display device. The front emission type fluorescent display device comprises an anode conductor formed of a metal film deposited on one surface of a glass substrate and a phosphor layer deposited on the anode conductor and is adapted to permit light emitted from the phosphor layer due to impingement of electrons thereon to be observed through the glass substrate and anode conductor from the other surface side of the glass substrate.
2. Description of the Prior Art
In a front emission type fluorescent display device, wiring conductors including anode terminals (hereinafter referred to as "wiring conductors") and anode conductors are formed by subjecting a film of a conductive material deposited on a substrate by means of sputtering, vapor deposition or the like to etching by photolithography to form a desired pattern. Accordingly, the wiring conductors and anode conductors are both formed of the same conductive material.
Such a conductive film for use in a flourescent display device is generally divided into a transparent conductive film such as an ITO film, a nesa film or the like and a metal film such as an aluminum film. When anode conductors are formed of the metal film, at least a part of the anode conductors is constructed to include a conductive section formed into a mesh-like or pectinate shape and gaps therebetween so that the anode conductors may be of light-permeability. This makes it possible to observe luminous display of phosphor layers deposited on the light-permeable anode conductors hereinafter referred to as "anode conductors") through the substrate and the anode conductors.
When the substrate of the front emission type fluorescent display device in which the wiring conductors and anode conductors are formed of the metal film is viewed from a display side, the wiring conductors and mesh-like anode conductors are observed as a specular surface on the opposite side of a transparent substrate. This causes incident light to be reflected on the specular surface at a positive reflectance of 80% or more, to thereby deteriorate visibility of a display section, particularly, under high illuminance.
In order to avoid such a problem, applicant has proposed in Japanese application No. 58-222714 filed Nov. 26, 1983 a front emission type fluorescent display device having a colored antireflection film interposed between wiring conductors and anode conductors each formed of a metal film and a substrate as shown in FIG. 3.
In FIG. 3, reference numeral 1 designates a glass substrate. The glass substrate 1 has an antireflection film 2 of a light-permeable material of low permeability, such as, for example, molybdenum oxide deposited on one surface thereof. On the antireflection film 2 is arranged a metal film 3 forming wiring conductors and anode conductors.
External light, for example, incident light 4 introduced from a light source 4a to the substrate 1 is partially reflected on an upper surface of the antireflection film 2. The remaining of the light is introduced into the antireflection film 2 and then reflected on an interface between the antireflection film 2 and the metal film 3 and passes through the antireflection film 2 and substrate 1 to the exterior, during which a part of the light is reflected on an upper surface of the substrate 1 and returned into the substrate.
In this manner, the external light is reflected on the substrate 1 and antireflection film 2 several times. In the course of the reflection, it is absorbed and diffused, which makes positive reflectance decrease and the specular surface of the metal film 3 hard to observe. In FIG. 3, the antireflection film 2 may be formed of a material having a low reflectance such as chromium oxide.
However, materials used for the antireflection film 2 are generally apt to lack stability. For example, chromium oxide and molybdenum oxide are both oxides of a transition metal element, which is reduced during a calcination step in the manufacturing of a fluorescent display device and deteriorate desired antireflection property. Also, the fluorescent display device described above has another disadvantage of failing to exhibit a sufficient antireflection effect, because the antireflection depends on only the absorption and diffusion of external light by the antireflection film.